This invention relates to novel naphthalocyanine derivatives, process for producing them, optical recording medium using them, and process for producing said optical recording medium.
Recently, the use of semiconductor laser light has been proposed as a means for writing-in or reading-out in compact disk, video disk, liquid crystal display, optical letter-reading machine, etc. or as a light source of electrophotography. Writing or reading by means of semiconductor laser light indispensably requires a substance capable of absorbing semiconductor laser light or near infrared light.
As the organic dye absorbing near infrared light, cyanine dye has been well known hitherto. Metal complexes of oximes and thiols and aminated quinone derivatives are also known as dyes capable of absorbing near infrared light (Yuki Gosei Kagaku Kyokai-shi, Vol. 43, Page 334 (1985); Shikizai Kyokai-shi, Vol. 53, Page 197 (198); and Shikizai Kyokai-shi, Vol. 58, Page 220 (1985)).
However, the use of cyanine dye is restricted in many points because of its extremely low fastness to light. Metal complexes of oximes and thiols are also disadvantageous in that the metal is eliminated from complex in some media and thereby the ability to absorb near infrared light is lost. Aminated quinone derivatives also have a problem that their ability to absorb near infrared light is quite low.
As a material capable of overcoming these disadvantages, naphthalocyanine derivatives have recently been disclosed. However, so far known unsubstituted metal naphthalocyanines (Zhurnal Obschei Khimii, Vol. 39, Page 2554 (1969); Mol. Cryst. Liq. cryst., Vol. 112, Page 345 (1984)) are quite difficult to purify because they are insoluble in organic solvents. Recently, synthesis of naphthalocyanine derivatives soluble in organic solvent have been reported (Japanese Patent Application Kokai (Laid-Open) 60-23451, 60-184565, 61-215662, 61-215663). However, solubility of these compounds in saturated hydrocarbon solvents is very low, though they are generally soluble in aromatic hydrocarbons and halogen-containing solvents, and therefore their film cannot directly be formed on polymethyl methacrylate and polycarbonate substrates by the wet coating method without providing a protecting layer on the substrate. Thus, it is desired to discover a naphthalocyanine compound exhibiting an excellent solubility in saturated hydrocarbon solvents.
Further, these naphthalocyanine derivatives are disadvantageous in that their absorption greatly varies depending on the kind of solvent, their concentration in solution and temperature so that their ability to absorb semiconductor laser light much decreases in a high-concentration solution or in solid film, and that their reflectance, important to the reading out of information recorded in an optical disk when a reflected light is used, is very low in the semiconductor laser region (780-830 nm).
In Japanese Patent Application Kokai (Laid-Open) 61-235188, only two compounds are disclosed as naphthalocyanine compounds having a high reflectance, and conception of their syntheses are mentioned in Japanese Patent Application Kokai (Laid-Open) 61-177287 and 61-77288. However, only a few working examples are presented in these patent gazettes, and only a few compounds can be synthesized actually in accordance with their descriptions. For example, in Reaction Scheme I (line 1, right upper section, page 8) of Japanese Patent Application Kokai (Laid-Open) 61-177288, the starting compound represented by the following formula: ##STR2## has too high a solubility when Xn is a long chain alkyl group, and this starting compound cannot be isolated from reaction mixture in its synthesis. Furthermore, in the synthesis of its raw material represented by the following formula: ##STR3## the reaction yields a complicated reaction mixture from which the raw material cannot be isolated and purified easily and is unusable in the intended naphthalocyanine synthesis. On the other hand, Reaction Scheme II (line 3, right upper section, page 8) of Japanese Patent Application Kokai (Laid-Open) 61-177288, is a nucleophilic reaction of naphthalocyanine ring resembling Friedel-Crafts reaction and not suitable for introduction of alkoxyl group, alkylthio group and amino group. In Reaction Scheme III (line 5, right upper section, page 8) of Japanese Patent Application Kokai (Laid-Open) 61-177288, the starting compound cannot be purified and the product is a very complicated mixture difficult to purify, so that the process is unsuitable for isolating a high-purity product. Further, the reaction itself is disturbed by the influence of hydroxyl group attached to Si in starting material, and the reaction cannot be advanced toward the intended direction. As has been mentioned above, it has been necessary to discover a new synthetic process in order to synthesize a naphthalocyanine compound soluble in organic solvent, excellent in the characteristic properties as optical recording medium and having a long chain alkyl group on the naphthalocyanine ring.